The present invention relates to a process for the manufacture of polymers is bead form from water-soluble, ethylenically unsaturated monomers by the inverse suspension polymerization process, in which an aqueous solution of the monomers is suspended in an inert hydrophobic liquid and polymerized therein, in the presence of a polymerization initiator and a protective colloid, to give polymeric products in bead form.
This process for the manufacture of polymers in bead form from water-soluble, ethylenically unsaturated monomers is disclosed in German Pat. No. 1,081,228. For the purpose of carrying out the process in practice, the correct choice of a suitable protective colloid is critical. The protective colloids stabilize the water-in-oil emulsions and influence the size of the polymer beads. Examples of protective colloids employed are sorbitan esters, eg. sorbitan monostearate and sorbitan monooleate, ethoxylated fatty acid amides, fatty acid esters of glycerol, sorbitan sesquioleate and sorbitan monooleate together with dicalcium phosphate or hydroxyapatite or silicates. A further group of conventional protective colloids comprises block polymers or graft polymers which contain at least one polymeric hydrophilic portion and one polymeric hydrophobic portion in the molecule. The process of inverse suspension polymerization permits the manufacture of polymers of particularly high molecular weights and further provides the possibility of removing the water directly by azeotropic distillation from the system, given a suitable choice of the auxiliary phase.
During the polymerization, the aqueous phase of the water-in-oil dispersion passes through a very tacky state. Even after completion of the polymerization, the suspended water-containing polymer is not non-tacky. Hence, polymer particles can stick to one another and to the walls of the vessel during the polymerization or during azeotropic dehydration following the polymerization. In extreme cases this phenomenon can reach such proportions that the entire polymer sticks together in one coherent mass which clings to the stirrer and the walls. The conventional protective colloids have the disadvantage that they do not prevent the build-up of deposits on the walls of the polymerization apparatus and on the stirrer.
It is an object of the invention to provide protective colloids for the initially described inverse suspension polymerization process, by means of which the disadvantages of the conventional protective colloids are very substantially avoided.